Methods and systems for assisted direct start control

ABSTRACT

Method and systems are provided for controlling a vehicle system including an engine that is selectively deactivated during engine idle-stop conditions. One example method comprises, adjusting a brake torque applied to a deactivated rotating engine after an engine restart request, the brake torque applied to slow the engine to at least a predetermined threshold speed without stopping the engine, and engaging a starter to the still rotating engine to increase the engine speed and restart the engine.

FIELD

The present application relates to methods and systems for controllingan engine shut-down and a subsequent engine restart.

BACKGROUND AND SUMMARY

Vehicles have been developed to perform an idle-stop when idle-stopconditions are met and automatically restart the engine when restartconditions are met. Such idle-stop systems enable fuel savings,reduction in exhaust emissions, reduction in noise, and the like.

Engines may be restarted from the idle-stop condition automatically,without receiving an operator input, for example, in response to engineoperating parameters falling outside a desired operating range.Alternatively, engines may be restarted from the idle-stop condition inresponse to a vehicle restart and/or launch request from the operator.

However, the inventors have recognized several potential issues withsuch a system. As one example, if a driver has a change of mind whilethe engine is being shut down (e.g., still spinning down) and wishes toimmediately restart the engine, a desirable fast restart may not bepossible. Specifically, the driver may have to wait for the engine tostop rotating completely before the engine starter can be re-engaged. Assuch, this may substantially increase the change of mind restart timeand thus degrade the quality of the restart operation.

Thus in one example, the above issue may be addressed by a method ofcontrolling a vehicle system including an engine that is selectivelydeactivated during engine idle conditions, the method comprising,adjusting a brake torque applied to a deactivated rotating engine afteran engine restart request, the brake torque applied to slow the engineto at least a predetermined threshold speed without stopping the engine,and engaging a starter to the still rotating engine to increase theengine speed and restart the engine.

In one example, during the execution of an engine idle-stop operation, adriver may change their mind and request an immediate restart (e.g., byreleasing a brake pedal). In response, a controller may be configured torestart the engine via a starter motor with the engine still spinning,that is, without necessitating a complete engine stop. As such, anengine starter may be configured to be engaged at engine speeds abovezero, for example, at or below a predetermined threshold speed (such asat or below 50 rpm, or at or below 100 rpm). If the engine speed at thetime of restart request is at or below the predetermined threshold, thestarter may be immediately engaged to the still rotating engine toincrease engine speed and enable an immediate restart. Alternatively, ifthe engine speed at the time of restart request is above thepredetermined threshold, the controller may adjust a brake torque thatis applied to the engine to more rapidly and forcefully slow the engineto at least the predetermined threshold starter engagement speed. Oncethe threshold speed is attained, the starter may be engaged to the stillrotating engine to increase engine speed and restart the engine. Thebrake torque employed may include one or more of a reverse torque (forexample, by clutching in the alternator or the AC compressor), an outputshaft torque or a transmission drag torque (for example, by clutching inthe transmission), a gas torque (for example, by deactivating thecylinders), or a combination thereof. By expediting engine slow-down tothe starter threshold speed and engaging the starter to the stillrotating engine, a rapid restart and vehicle launch may be achievedwithout requiring prior complete engine shut-down. However, it will beappreciated that if a prior engine full stop is desired (for example, asdetermined by the driver, or by the engine controller), a restart mayalternatively be performed only after fully stopping the engine, butagain optionally using a brake torque to rapidly slow the engine torest.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example vehicle system layout, including details of avehicle drive-train.

FIG. 2 shows a high level flow chart for executing an idle-stopoperation.

FIG. 3 shows a high level flow chart for a executing a restartoperation, in response to a driver's change of mind during an idle-stopoperation, according to the present disclosure.

FIGS. 4A-C shows maps with a plurality of graphs explaining exampleengine restart procedures in response to a driver change of mind,according to the present disclosure.

DETAILED DESCRIPTION

The following description relates to systems and methods for performingan engine restart operation responsive to a driver change of mindrestart request. As such, the restart request may be received during theexecution of an engine idle-stop operation where the engine has not yetstopped. In response to the restart request, a controller may beconfigured to control operation of a variety of engine drive trainand/or accessory components, such as those illustrated in FIG. 1, tothereby adjust a brake torque applied to the engine to slow the enginespeed. As shown in FIGS. 2-3, the brake torque may enable engine speedto be rapidly lowered to at least a predetermined starter thresholdspeed wherefrom an engine starter may be engaged and an immediatevehicle restart may ensue. Specifically, once the predeterminedthreshold is attained, the starter may be engaged to the still rotatingengine to increase engine speed and restart the engine. In this way, asfurther elaborated in FIGS. 4A-C, an engine may optionally be re-startedwithout first bringing the engine to a complete stop. Furthermore, thetime required for restarting an engine in response to a driver change ofmind can be significantly reduced.

FIG. 1 shows a block diagram layout of a vehicle system 10, including avehicle drive-train 20. Drive-train 20 may be powered by engine 22. Inone example, engine 22 may be a gasoline engine. In alternateembodiments, other engine configurations may be employed, for example adiesel engine. Engine 22 may be started with an engine starting system24, including a starter. In one example, the starter may be amotor-driven (or battery-driven) starter. In another example, thestarter may be a powertrain drive motor, such as a hybrid powerplantconnected to the engine by way of a coupling device. The coupling devicemay include a transmission, one or more gears, and/or any other suitablecoupling device. The starter may be configured to support engine restartat or below a predetermined near zero threshold speed, for example at orbelow 50 rpm, or 100 rpm). Alternatively, the predetermined thresholdspeed may be a speed range, for example 50 to 100 rpm. Further, thethreshold speed (or speed range) may be adjusted responsive to operatingconditions, such as engine temperature. In one example, when the enginetemperature is relatively cold, the threshold speed may be adjusted to alower value due to lower current availability and lower frictionalresistance from the starter. In another example, when the enginetemperature is relatively hot, the threshold speed may be adjusted to ahigher value due to higher current availability and higher frictionalresistance from the starter. In either case, an engine controller mayadjust the threshold speed to avoid operating the engine in itsresonance region. As such, the resonance region may be above the crankspeed but below the idle speed. Engine 22 may further generate or adjusttorque via torque actuator 26, such as a fuel injector, throttle, etc.Additionally, in the case of a hybrid vehicle, the powertrain may beused to slow or speed the engine, as desired.

An engine output torque may be transmitted to torque converter 28 todrive an automatic transmission 30 by engaging one or more clutches,including forward clutch 32, where the torque converter may be referredto as a component of the transmission. As such, a plurality of suchclutches may be engaged, as needed. The output of the torque convertermay in turn be controlled by torque converter lock-up clutch 34. Whentorque converter lock-up clutch 34 is fully disengaged, torque converter28 transmits torque to automatic transmission 30 via fluid transferbetween the torque converter turbine and torque converter impeller,thereby enabling torque multiplication. In contrast, when torqueconverter lock-up clutch 34 is fully engaged, the engine output torqueis directly transferred via the torque converter 28 clutch to an inputshaft (not shown) of transmission 30. Alternatively, the torqueconverter lock-up clutch 34 may be partially engaged, thereby enablingthe amount of torque relayed to the transmission to be adjusted. Acontroller 40 may be configured to adjust the amount of torquetransmitted by the torque converter by adjusting the torque converterlock-up clutch in response to various engine operating conditions, orbased on a driver-based engine operation request.

Torque output from the automatic transmission 30 may in turn be relayedto wheels 36 to propel the vehicle. Specifically, automatic transmission30 may adjust an input driving torque at the input shaft (not shown)responsive to a vehicle traveling condition before transmitting anoutput driving torque to the wheels.

Further, wheels 36 may be locked by engaging wheel brakes 38. In oneexample, wheel brakes 38 may be engaged in response to the driverpressing his foot on a brake pedal (not shown). In the same way, wheels36 may be unlocked by disengaging wheel brakes 38 in response to thedriver releasing his foot from the brake pedal.

A mechanical oil pump (not shown) may be in fluid communication with theautomatic transmission 30 to provide hydraulic pressure to engage thevarious clutches, such as forward clutch 32 and/or torque converterlock-up clutch 34. The mechanical oil pump may be operated in accordancewith torque converter 28, and may be driven by the rotation of engine 22or the transmission input shaft, for example. Thus, the hydraulicpressure generated in the mechanical oil pump may increase as an enginespeed increases, and may decrease as an engine speed decreases. Anelectric oil pump (not shown), also in fluid communication with theautomatic transmission 30 but operating independent from the drivingforce of the engine 22 or transmission, may be provided to supplementthe hydraulic pressure of the mechanical oil pump. The electric oil pumpmay be driven by a battery-driven motor (not shown).

Vehicle system components outside of the drivetrain, that is accessorycomponents, may include an alternator 42, a battery 46 and an airconditioner 48. Alternator 42 may be configured to convert themechanical energy generated while running engine 22 to electrical energyfor storage in battery 46. Alternator 42 may include an alternatorclutch 44. As such, when the alternator clutch 44 is engaged, torqueoutput from the running engine may be relayed to alternator 42 along analternator input shaft (not shown). However, as further elaboratedherein, under certain conditions, for example when the engine isundergoing an idle-stop, controller 40 may be configured to selectivelyengage (at least partially) alternator clutch 44 and relay the accessorytorque generated in alternator 42 to slow down engine 22. That is, theaccessory torque may be used as a reverse torque.

Air conditioner (AC) 48 may include a compressor (not shown) and acompressor clutch 50. As such, when the compressor clutch 50 is engaged,torque output from the running engine may be relayed to the ACcompressor, for compressing air and running the AC. However, as furtherelaborated herein, under certain conditions, for example when the engineis undergoing an idle-stop, controller 40 may be configured toselectively engage (at least partially) compressor clutch 50 and relaythe accessory torque generated in the compressor to slow down engine 22.That is, the accessory torque may be used as a reverse torque.

Controller 40 may be configured to receive inputs from engine 22 andaccordingly control a torque output of the engine and/or operation ofthe torque converter, transmission, brakes, alternator and/or AC. As oneexample, a torque output may be controlled by adjusting a combination ofspark timing, fuel pulse width, fuel pulse timing, and/or air charge, bycontrolling throttle opening and/or valve timing, valve lift and boostfor turbo- or super-charged engines. In the case of a diesel engine,controller 40 may control the engine torque output by controlling acombination of fuel pulse width, fuel pulse timing, and air charge. Inall cases, engine control may be performed on a cylinder-by-cylinderbasis to control the engine torque output.

When idle-stop conditions are satisfied, controller 40 may apply a braketorque to stop the engine by controlling operation of drivetrain and/oraccessory components. The applied brake torque may gradually bring theengine to a full stop. However, in some situations, during the executionof the idle-stop operation, the driver may change his mind and decide toimmediately restart the engine and/or launch the vehicle. As such, thestarter may not be engageable unless the engine speed is at or below thepredetermined starter threshold speed (which may depend on variousfactors such as temperature, etc.). Furthermore, the engine controllermay delay restarting the engine until the engine speed is out of aresonance region, which may be a range of engine speeds. If the enginespeed at the time of change of mind (COM) restart request is at or belowthe threshold speed, controller 40 may immediately engage the starter tothe spinning engine to increase engine speed and restart the engine.However, if the engine speed at the time of restart request is above thethreshold speed, controller 40 may adjust operation of drivetrain and/oraccessory components to adjust the brake torque to the engine to therebyrapidly and deliberately reduce the engine speed to at least thethreshold speed. After the threshold speed is attained, the starter maybe engaged to the rotating engine and a restart may be achieved. Herein,the engine speed may be substantially immediately (and not gradually)reduced to the threshold speed to expedite engine restart.

In one example, adjusting the brake torque applied to the engine toexpedite engine slow-down may include increasing the brake torqueapplied to the engine. This may be desirable when the difference betweenthe engine speed at the time of restart request and the predeterminedthreshold speed is relatively larger. Herein, by increasing the braketorque, the engine speed may be immediately reduced without adverselyaffecting engine components. In another example, adjusting the braketorque applied to the engine to expedite engine slow-down may includedecreasing the brake torque applied to the engine. This may be desirablewhen the difference between the engine speed at the time of restartrequest and the predetermined threshold speed is relatively smaller.Herein, a further increase in the brake torque may adversely affectengine components, such as drivetrain components, and degrade engineperformance. Thus, by decreasing the brake torque, the engine speed maybe rapidly reduced to the threshold speed without affecting vehicleperformance.

As such, the brake torque applied to the engine may include one or moreof a reverse torque, a transmission drag torque, and a gas torque. Inone example, applying a reverse torque to brake engine speed may includeengaging a clutch of the alternator clutch and/or engaging a clutch ofthe air conditioner compressor. In another example, if the vehicle isequipped with an accessory shaft-to-heat device (such as a sheargenerating device or a coulomb torque device), clutching in of thedevice may optionally or additionally be employed to enable a fast andsmooth engine spin-down. Herein, the heat may be transferred to theengine oil or the engine coolant.

When applying a transmission drag torque to brake engine speed, at leastone transmission hydraulic component, such as a forward clutch of thetransmission and/or a torque converter clutch, may be engaged with thetransmission in an engaged gear, such as a first gear. In one example,the torque converter can be used to transmit a drag torque generated bythe stopped vehicle wheels through the gears of the transmission via thetransmission forward clutch. In other words, an in-gear transmission maybe used to apply a braking drag torque on the engine, wherein the amountof torque applied can be modulated via slipping of a transmissionclutch, such as the forward clutch and/or torque converter clutch. Inanother example, a larger drag torque can be generated by increasingengagement of at least one (or both) of the torque converter clutch andthe transmission forward clutch. For example, if the transmissionforward clutch and torque converter clutch were fully engaged, and thewheels were held fixed to the ground via friction and/or the wheelbrakes, then a maximum drag torque can be applied to the engine(assuming the wheels do not break free from the ground). Similarly, thedrag torque can be reduced by increasing the slip of at least one orboth of the torque converter clutch and transmission forward clutch. Assuch, by using a transmission drag torque to expedite engine spin-down,a controller may also be able to limit the engine's tendency to pumpoxidant through the catalyst (of the emission control device) andthereby limit the amount of reductant subsequently required to return tothe desired operating condition.

Thus, in one example, controller 40 may maintain forward clutch 32 in anengaged state, at least during the engine spin-down, and may start toengage torque converter lock-up clutch 34 (if it is not already engaged)to thereby allow an increased external frictional (drag) torque to beapplied. In this example, the level of engagement of the torqueconverter lock-up clutch (that is, whether the clutch is fully engaged,or partially engaged) may be adjusted in response to the desiredspin-down time to thereby adjust the level of the drag torque responsiveto the engine speed and thereby control the spin-down of the engine.Alternatively, the controller 40 may maintain the engagement state ofthe torque converter lock-up clutch 34 at a fixed value and modulate theengagement state of the automatic transmission forward clutch 32 byadjusting the hydraulic pressure supplied to the forward clutch.Alternatively still, controller 40 may modulate the engagement state ofboth the torque converter lock-up clutch as well as the forward clutchto thereby adjust the drag torque applied to reduce the engine speed tozero. Controller 40 may select between the possible alternatives basedon engine operating conditions, clutch conditions (for example, the wearand tear level of forward clutch 32 and torque converter lock-up clutch34), the response time desired for engine spin-down, etc.

Engine spin-down may also be expedited by applying a gas torque as abraking torque to the engine via cylinder deactivation mechanisms. Inone example, at least an intake valve of the designated cylinder(s) maybe closed while leaving the exhaust valves open. The substantially zeroair flow and the lack of gas in the cylinder forcefully reverses theengine, enabling a rapid engine spin-down without causing degradednoise, vibration and harshness (NVH). In another example, ignitiontiming (that is, spark timing) may be advanced (for example,over-advanced). Specifically, controller 40 may wait for manifoldpressure (MAP) to fall, due to throttle shuttling, below a predeterminedthreshold, and then adjust the intake valve timing to a maximally lateintake valve closure (to thereby compress as little as possible).Subsequently, spark timing may be advanced to a time significantlybefore MBT (e.g., peak torque spark timing for the current engineconditions) to enable rapid engine speed reversal. As such, use of sparktiming advance may be selected at light engine loads.

It will be appreciated that, in still other examples, controller 40 maybe configured to employ any combination of reverse torque, transmissiondrag torque, and gas torque to adjust the braking torque and expediteengine slow down to the predetermined starter speed threshold inresponse to the driver change of mind restart request. Controller 40 mayselect between the possible alternatives based on engine operatingconditions, clutch conditions (for example, the wear and tear level ofthe different clutches), the response time desired for engine spin-down,etc.

Now turning to FIG. 2, a routine 200 is described for performing anidle-stop operation in the vehicle system of FIG. 1. At 202, it isconfirmed if idle-stop conditions 203 have been met. Any or all of theidle-stop conditions 203, as further described herein, may be met for anidle-stop condition to be confirmed. For example, at 210, the enginestatus may be determined. Herein it may be verified that the engine isoperating (e.g., carrying out combustion). At 212, the battery state ofcharge may be determined. In one example, if the battery state of chargeis more than 30%, it may be determined that an engine idle-stop mayproceed and that recharge may not be required. At 214, it may beverified that the vehicle running speed is within a desired range. Inone example, the desired range may be no more than 30 mph. At 216, anair-conditioner status may be assessed and it may be verified that theair conditioner did not issue a request for restarting the engine, asmay be requested if air conditioning is desired. At 218, the enginetemperature may be estimated and/or measured to determine if it iswithin a selected temperature range. In one example, the enginetemperature may be inferred from an engine coolant temperature and anengine idle-stop condition may be selected when the engine coolanttemperature is above a predetermined threshold. At 220, a throttleopening degree may be determined using a throttle opening degree sensor.In one example, the sensor reading may be used to verify that a starthas not been requested by the vehicle driver. At 222, the driverrequested torque may be estimated to confirm that it is less than apredetermined threshold value. At 224, a brake sensor status may beread. In one example, the brake sensor may read the status of the brakepedal and verify that the brake pedal has been pressed. At 226, theengine speed may be determined. At 228, the input shaft rotation number(Ni) may be determined.

If idle-stop conditions are not met, the routine may end. However, ifany or all of the idle-stop conditions are met, then at 204, thecontroller may initiate execution of the idle-stop operation and proceedto deactivate the engine. As such, this may include shutting off fueland/or spark to the engine. While the idle-stop operation is under way,at 206, it may be determined whether a driver change of mind (COM) hasoccurred or not. That is, it is determined whether the driver hasdecided to discontinue the engine idle-stop operation (e.g., via releaseof the wheel brakes) and restart the engine instead. If no driver COM isdetermined, then at 208, controller 40 may proceed to complete theidle-stop operation started at 204, following which, the engine may bemaintained in idle-stop until restart conditions are satisfied.

If a driver COM is determined at 206, a COM-based restart may beperformed at 209. Herein, as further elaborated with reference to FIG.3, it may be determined whether an engine restart is desired with theengine still, or whether the restart is desired after fully stopping theengine. Accordingly, and further based on the present engine speed, abraking torque may be applied and adjusted to expedite engine slow-downto a threshold speed, wherefrom a starter may be engaged and a rapidengine restart may be achieved.

Now turning to FIG. 3, a routine 300 is described for performing aCOM-based engine restart operation in the vehicle system of FIG. 1. Assuch, the COM-based restart request may be received during the previousidle-stop operation and while the engine is not yet stopped. That is,the engine may be deactivated (with fuel injection and/or sparking shutoff), but still rotating. At 302, it is confirmed whether a COM-basedrestart without an engine full stop has been requested. That is, it isdetermined whether a restart is desired while the engine is stillspinning. During a first restart condition where no COM-based restartwith full engine stop is requested, at 304 (and as further depicted inFIG. 4A), the routine may proceed to apply a brake torque to the engine,wait for the engine to fully stop, engage a starter to the stoppedengine and restart the engine. Herein, an immediate restart may not beattainable. A controller may select the COM-based restart with enginefull stop based on starter motor conditions, battery state of charge,etc.

If a COM-based restart without engine full stop is requested, at 306,the engine speed (N_(e)) may be measured and/or estimated. At 308, it isdetermined whether the engine starter may be engaged (and hence arestart operation may be possible) at the estimated engine speed.Specifically, it is determined if the engine speed is at or below thepredetermined starter threshold speed (for example, at or below 50 or100 rpm). Alternatively, it may be determined whether the engine speedis within the predefined threshold speed range (for example, within 50to 100 rpm). As such, the engine starter may not be engaged at enginespeeds above the threshold speed (or speed range).

Thus, during a second restart condition wherein the engine speed at thetime of restart request is above the predetermined threshold, and it isdetermined that starter engagement is not possible at the current enginespeed, at 312, the engine controller may adjust the brake torque appliedto the engine to rapidly and deliberately slow the engine to at leastthe predetermined threshold speed. Once the predetermined thresholdspeed is attained, the starter may be engaged to the still rotatingengine to increase engine speed and perform a restart operation. Thatis, after the starter has been engaged, engine fuel and spark may bereactivated. As previously elaborated, the brake torque may be adjustedby controlling operation of a variety of vehicle drivetrain andaccessory components to thereby adjust a combination of a reversetorque, a transmission drag torque, and/or a gas torque. Specifically,the controller may adjust operation of a variety of transmissionclutches, such as a forward clutch and a torque converter lock-upclutch, to apply a transmission drag torque and/or adjust operation ofan alternator clutch and/or an AC compressor clutch, to apply a reversetorque. Further still, the controller may adjust cylinder deactivationmechanisms, such as by controlling operation of cylinder intake valvesand/or spark timing, to apply a gas torque to expedite engine slow-down.In this way, using a combination of torques to apply a brake torque,engine speed may be deliberately and swiftly reduced to a starterthreshold speed wherefrom the starter may be re-engaged for a rapidengine restart. Such an operation is depicted below with reference toFIG. 4B.

During a third restart condition wherein the engine speed at the time ofrestart request is at or below the predetermined threshold, and it isdetermined that starter engagement is possible at the current enginespeed, at 310, the brake torque may be removed and the starter may beengaged to the still rotating engine to increase engine speed andexecute a restart. That is, after the starter has been engaged, enginefuel and spark may be reactivated. Such an operation is also depictedbelow with reference to FIG. 4C.

In this way, an expedited restart may be achieved in response to adriver change of mind restart request received in the midst of anidle-stop operation and where the engine is not yet stopped. Byadjusting a brake torque applied to the engine to deliberately slowengine speed to a starter threshold, a change of mind restart requesttime can be substantially reduced.

FIGS. 4A-C depict maps 400 a-c with a plurality of graphs depictingexample shutdown and restart scenarios for further explaining thevarious COM-based restart operations (as discussed in FIG. 3) of thepresent disclosure.

FIG. 4A depicts a COM-based restart operation with engine full stop. InFIG. 4A, map 400 a shows an indication of idle-stop status in firstgraph 402. Second graph 404 depicts the brake torque applied to theengine. As such, this may represent any combination of reverse torque,transmission drag torque, and gas torque, applied to the engine. Thirdgraph 406 represents variations in engine speed (N_(e)) during thedepicted idle-stop or restart operations.

Herein, at t₁, and as indicated by graph 402, an idle-stop request maybe confirmed (for example, by confirming idle-stop conditions) and anidle-stop operation may be initiated. Accordingly, as indicated by graph404, a brake torque may be applied on the engine to enable enginespin-down. The brake torque may be applied until an engine full stop isattained. As such, before idle-stop conditions are confirmed, that isbefore t₁, engine speed (as depicted by graph 406) may be at a highvalue. Upon application of the brake torque between t₁ and t₃, enginespeed may be gradually reduced, until engine full stop is attained att₃.

A driver change of mind (COM) restart request may be received during theidle-stop operation and while the engine is spinning down at t₂. Herein,since the restart is requested with engine full stop, an immediateengine restart may not be achievable. That is, a restart operation mayonly be initiated at t₃. As such, this may increase the COM restart time(for example, by more than 150 ms) when compared to restart operationsnot requiring a complete engine stop (as further elaborated in FIGS.4B-C).

In FIG. 4B, map 400 b depicts a COM-based restart operation whereinengine speed at an occurrence of restart request is above apredetermined starter threshold speed. An indication of idle-stop statusis provided in first graph 412. Second graph 414 depicts the braketorque applied to the engine while graph 416 represents variations inengine speed (N_(e)) during the depicted idle-stop or restartoperations.

As indicated in graph 412, an idle-stop operation may be initiated att₁. As indicated by graph 414, a brake torque may be immediately appliedon the engine to enable rapid engine spin-down. Consequently, a gradualreduction in engine speed (graph 416) may ensue. During the idle-stopoperation, and while the engine is still spinning, at t₂, a change ofmind (COM) restart request may be received. A controller may determinewhether the engine speed at the time of restart request is above orbelow a predetermined threshold speed (N_(min), dashed line 418) andaccordingly apply the brake torque. In one example, as indicated bygraph 416, the difference between engine speed at the time of restartrequest (t₂) and the predetermined threshold speed (N_(min)) may berelatively large. Accordingly, the brake torque applied to the engine(graph 414, solid line) may be increased (between t₂ and t₃) to expediteengine slow down (graph 416) to the threshold speed. Once the thresholdspeed is attained (t₃), an engine restart operation may be executed.

In another example, as indicated by dotted segment 417, the differencebetween engine speed at the time of restart request (t₂) and thepredetermined threshold speed (N_(min)) may be relatively small. Herein,a further increase in brake torque may degrade engine performance andaffect engine components. Accordingly, the brake torque applied to theengine (dotted segment 415) may be decreased (between t₂ and t₃) toexpedite engine deceleration (dotted segment 417) to the thresholdspeed. After the threshold speed is attained (t₃), an engine restartprocedure may be executed. In this way, the COM restart time may besubstantially reduced and brought within a desirable range (for example,within 300 ms).

FIG. 4C depicts a COM-based restart operation wherein engine speed at anoccurrence of restart request is below the predetermined starterthreshold speed. An indication of the idle-stop status is provided infirst graph 422. Second graph 424 depicts the net torque applied to theengine while graph 426 represents variations in engine speed (N_(e))during the depicted idle-stop or restart operations.

As indicated by graph 422, an idle-stop operation may be initiated att₁. As indicated by graph 424, a brake torque may be immediately appliedto the engine. In response, a gradual reduction in engine speed, asshown by graph 426, may ensue. During the idle-stop operation, and whilethe engine is still spinning, at t₂, a change of mind (COM) restartrequest may be received. A controller may determine that the enginespeed (as indicated by graph 426) at the time of restart request (t₂) isat or below the predetermined threshold speed (N_(min), dashed line418). Since the starter may be engaged at this speed, the brake torquemay be immediately removed. That is, a restart operation may beimmediately initiated at t₂, as indicated by a subsequent gradualincrease in engine speed (graph 426).

In this way, a change of mind based engine restart may be executedwithout requiring that the engine reach zero engine speed, if sodesired. By expediting engine deceleration to a threshold speedwherefrom a starter can be immediately engaged, a rapid restart andvehicle launch may be enabled. In doing so, change of mind restart timesmay be substantially reduced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method of controlling a vehicle system including an engine that isselectively deactivated during engine idle conditions, comprising:adjusting a brake torque applied to a deactivated rotating engine via aclutch after an engine restart request, the brake torque applied to slowthe engine to a predetermined threshold speed without stopping theengine; and engaging a starter to the still rotating engine to increaseengine speed and restart the engine.
 2. The method of claim 1 whereinthe starter is engaged at a predetermined engine speed.
 3. The method ofclaim 2 wherein the predetermined engine speed varies as engineoperating conditions vary.
 4. The method of claim 1 wherein engine fueland spark are reactivated to start the engine after the starter isengaged.
 5. The method of claim 3 wherein engine operating conditionsinclude engine temperature.
 6. A method of controlling a vehicle systemincluding an engine that is selectively shut-down during engineidle-stop conditions, the method comprising: receiving an engine restartrequest from an operator during an engine idle-stop operation where theengine is not yet stopped; adjusting a brake torque applied to theengine in response to the engine restart request, the brake torqueapplied to slow the engine to at least a predetermined threshold speed,including increasing the brake torque applied to the engine in responseto a first difference between engine speed at a time of restart requestand the predetermined threshold speed, and decreasing the brake torqueapplied to the engine in response to a second difference between enginespeed at the time of restart request and the predetermined thresholdspeed is relatively smaller, the first difference larger than the seconddifference; and once the at least a predetermined threshold speed isattained, engaging a starter to the still rotating engine to increaseengine speed and restart the engine.
 7. The method of claim 6 whereinthe brake torque applied to the engine includes applying one or more ofa reverse torque, a transmission drag torque, and a gas torque.
 8. Themethod of claim 7 wherein applying the reverse torque to the engineincludes engaging a clutch of an alternator and/or engaging a clutch ofan air conditioner compressor.
 9. The method of claim 7 wherein applyingthe transmission drag torque to the engine includes engaging at leastone transmission hydraulic component with a transmission in an engagedgear.
 10. The method of claim 9 wherein the at least one transmissionhydraulic component includes a forward clutch of the transmission and/ora torque converter clutch.
 11. The method of claim 7 wherein applyingthe gas torque includes at least one of closing at least an intake valveof a cylinder while leaving an exhaust valve open, adjusting intakevalve timing to a late intake valve closure, and advancing spark timing.12. The method of claim 6 wherein the predetermined threshold speed isless than 100 rpm.
 13. The method of claim 6 wherein the predeterminedthreshold speed is a speed range of 50-100 rpm.
 14. A method ofexpediting engine spin-down in an engine that is shut-down during engineidle-stop conditions and restarted during restart conditions, the methodcomprising: when an engine restart request is received from an operatorduring an engine idle-stop operation and where the engine is not yetstopped; during a first restart condition, applying a brake torque tothe engine, fully stopping the engine, and then engaging a starter tothe stopped engine to increase engine speed and restart the engine;during a second restart condition wherein engine speed at an occurrenceof a restart request is above a predetermined threshold, applying thebrake torque to the engine to slow the engine to at least apredetermined threshold speed, and after the at least a predeterminedthreshold speed is attained, engaging the starter to the still rotatingengine to increase engine speed and restart the engine; and during athird restart condition wherein the engine speed at the occurrence ofthe restart request is at or below the predetermined threshold, removingthe brake torque applied to the engine and engaging the starter to thestill rotating engine to increase engine speed and restart the engine.15. The method of claim 14 wherein the brake torque includes one or moreof a reverse torque, a transmission drag torque, and a gas torque. 16.The method of claim 15 wherein the reverse torque is achieved byengaging a clutch of an alternator and/or engaging a clutch of an airconditioner compressor, the transmission drag torque is achieved byengaging at least one of a forward clutch and a torque converter clutchof a transmission, and the gas torque is achieved by at least one ofclosing an intake valve of a cylinder while leaving an exhaust valveopen, adjusting intake valve timing to a late intake valve closure, andadvancing spark timing.
 17. The method of claim 14 wherein thepredetermined threshold speed is below 100 rpm.
 18. The method of claim14 wherein the predetermined threshold speed is a speed range of 50-100rpm.
 19. The method of claim 14 wherein applying the brake torque to theengine includes, increasing the brake torque applied to the engine whena difference between engine speed at the occurrence of the restartrequest and the predetermined threshold speed is relatively larger; anddecreasing the brake torque applied to the engine when the differencebetween engine speed at the occurrence of the restart request and thepredetermined threshold speed is relatively smaller.